1. Field of the Invention
The present invention relates to fluorescent lamp ballasts and more specifically to a digital control circuit that can achieve a real lamp power calculation in real time.
2. Description of the Background of the Invention
Analog ballast may achieve low cost and low power consumption. However, the performance of an analog ballast is limited due to effects of parasitic components and noise sensitivity on accuracy. Furthermore, the functionality, flexibility, and programmability of the analog ballast are also limited, since analog ballasts use multiple resistors and capacitors, which are difficult to implement using standard integrated circuit (IC) processing technology. Additionally, analog ballasts are complex and bulky.
Most dimmable high frequency (HF) electronic ballasts use analog ICs to control various operations of fluorescent lamps. These control operations may include preheat, ignition, burn standby, power regulation, and dimming. Some electronic ballasts may use standard CPUs or micro-controllers to control the operation of fluorescent lamps. For those ballasts the functionality, flexibility, and programmability is much improved.
However, due to the speed limitation, a standard CPU cannot process alternating current (AC) lamp signals in real time in order to obtain the required information, such as the phase of a current or voltage, peak current or voltage, real power, etc. This information is very important for a dimmable ballast control. Therefore, these kinds of digital ballasts have to sample more signals and require complicated signal condition circuits that are very difficult to integrate.
Furthermore, standard off-the-shelf micro-controllers with on-chip Analog-to-Digital (A/D) converters use slow on-chip A/D converters and are too slow to process the output of a high-speed A/D converter. Having slow on-chip A/D converters, the analog input signals are filtered externally, requiring additional external components. Additionally, filtering removes useful information from the input analog signal thereby limiting what can be regulated, e.g., real lamp power may not be regulated.
What is needed is a lamp signal processor able to use fast A/D converters, which may achieve the real lamp power calculation in real-time.
To achieve the real-time lamp signal processing, the present invention introduces a specific digital ballast control IC, designed and used in conjunction with analog digital ballasts.
The inventive digital lamp signal processor senses lamp current and lamp voltage in real time. These two signals are sufficient to obtain information, such as real lamp power calculation, necessary to control ballast operation and fault detection. The invention measures the phase of lamp current and voltage, the peak current and voltage, and calculates the average lamp current and voltage.
The inventive digital lamp signal processor eliminates the effect of parasitic capacitance of power wiring and a signal condition circuit. It may detect and control hard switching, and apply the over current and voltage protection. The invention directly processes AC signals allowing for simple and easily integrated single chip design.